Recording and controlling vehicle motion



Feb. 6, 1945. A G B METCALF 2,368,673

RECORDING AND CONTROLLING VEHICLE MOTION Filed March 16, 1940 6Sheets-Sheet l fil 4 Feb. 6, 1945. A, G B, METCALF 2,368,673

RECORDING AND GONTROLLING VEHICLE MOTION Filed March 16, 1940 6Sheets-Sheet 2 l RPLNE NGULAR DSPLCEMENT O.

ACTUAL o/sPLAcsME/vr Reco/ese co/vr/eoLLfo MEA/v PATH nuo/3ER Pos/r/o/vANGULAR DISPLACEMENT' 'U- ANGULAR vsLoc/ry REFER/e5@ ro /MEA/v op 25,120VALUE RUDDER POSITION ANGULAR ACCELERAT/ON REFERRED T0 MEAN 0R ZEROVALUE RUDDER POS! T/ON Feb. 6, 1945. A. G. B. METCALF 2,368,673

RECORDING AND CONTROLLING VEHICLE MOTION Filed March 16, 1940 6Sheets-Sheet 3 Feb. 6, 1945. A. G. B. METcALF RECORDING AND CONTROLLINGVEHICLE MOTION' Filed Maron 16, 1940 e sheets-sheet l IYIIIIII,

' 7u! armar Feb. S, 1945. A. G. B. METCALF 2,368,673

RECORDING AND CONTROIILING VEHICLE MOTION Filed Marbh 16,- 1940 6Sheets-Sheet 5 Feb. s, m5., A, 'B METCA'LF 2,368,673

RECORDING AND CONTROLLING VEHICLEMOTION Filed .Marc 16, 1940 6Sheets-Sheet 6 Patented Feb. 6, 1945 RECORDING AND CONTROLLING VEHICLEMOTION Arthur G. B. Metcalf, Milton, Mass. Application March 16, 1940,Serial No. 324,339

Claims.

My invention relates to a method of and apparatus for detecting, andrecording or eiecting a control response related to, motion which avehicle, for example an airplane or similar object in motion, may have.

One of the objects of my invention is to effect a control response whichbears a relation, not necessarily linear, to the instantaneous value ofthe angular velocity-time function referred t5 any selected axis or axesor its mathematical time-integrals or time-derivatives, such as theangular acceleration.

Other objects of the invention are detecting the variation with time ofthe angular velocity above a given axis of a vehicle by means of aprecessing gyroscope, detecting the variation with time ofthe angularacceleration about a given axis of a vehicle by means of a torsionalseismic element and recording such variations or using them to controldamping moments or forces suppressing undesirable motion of an airplane,apart from course or -directional control, such stabilizing controlbeing combined'with, or superimposed upon, the conventional manual orautomatic course control.

Another object of my invention is to provide a self-contained portabledevice capable of recording on a illm an amplitude-time record of theangular velocityl of a vehicle such as an airplane.

A further object of the invention is to provide a method and aninstrument for recording the motion of an airplane after disturbances,in a manner which provides, in the form of an oscillogram, the values 0fthe period and the damping coeiiicient characteristic of the motion as ameans of studying the dynamical stability of the motion of airplanes orother vehicles.

Still another object of my invention is to provide a means of selectingand detecting simultaneously the variation with time, of a number ofcomponents of angular velocity or acceleration referred to anyconvenient system of reference aXeS.

Other features are especially suitable detecting, recording and controlmechanism, an amplitude control for varying a torque or moment opposingthe -precessional motion of a gyroscope, a'torsional seismic elementAarranged for the detection of angular accelerations and for applyingthem to recording and control' mechanism, and arrangements forsimultaneously applying to an airplane, Yon the one hand, restoring ordamping moments which are related to the instantaneous value o'f angularvelocity` or acceleration andron the other hand, effects proportionateto the average deviations from a set course, whether manually orautomatically controlled. The invention also contemplates thesimultaneous detecting and recording of airplane angular velocity oracceleration about all three axes, and automatic ight stabilizingcontrolwith arrangements analogous to those for recording the flightcharacteristics.

These and other objects, aspects and features of the invention will beapparent from the description of a practical embodiment of the in,-vention illustrating its genus by way of example and referring todrawings in which:

Fig. 1 is a scheme of the axes conventions herein used;

Fig. 2 shows displacement-time; velocity-time; and acceleration-timecharacteristics of .the disturbed airplane motion;

Figs. 3, 3, 4 and '15 are diagrams illustrating l various types ofairplane motion;

Fig. 6 is a diagram illustrating the arrangement, according to theinvention, of gyroscopic detectors referred to axes conventions of Fig.1;

Fig. '7 is an isometric view of a detector and recording instrumentlaccording to the invention;

Fig. 8 is a section on line 8-8 of Fig..'7;

Fig. 9 is a section on line 9-9 of Fig. 7

Fig. 10 is a section on line lll-l0 of Fig. 9;

Fig. 11 is a sectional view on line H-ll of Fig. 9; f

Fig. 12 is a view similar to Fig. 11 but with the recording leverdisplaced;

Fig.'13. is .a section on line I3-I3 oi' Fig. 9; Fig. 14 is a detail,partly in section, of the recording device shown in Fig. 9;

Fig. 15 shows a modification of the amplitude adjustment device shown inFig. 10;

Figs. 16 and 17 are diagrams illustrating the operation of amplitudeadjustment devices according to Figs. 15 and 10, respectively;

Fig. 18 is a circuit diagram of apparatus according to Fig. 7;

Fig. 19 is a diagram showing a hydraulic air- Fig. 21 is a diagram ofacceleration Adetectf ing apparatus according to the invention;

Fig. 22 is a diagram of the relation between airplane angular deflectionamplitude and that indicated by the torsional seismic element shown inFig. 21;

Fig. 23 is a side view, with the housing in axial section. of apparatusaccording to Fig. 21;

tion oi.' air masses in the air through which it4 flies, (2) lack ofhomogeneity in the structure of Y the atmosphere, andl (3) variation incontrol setting or in propeller thrust. The airplane, therefore, iscontinually executing that motion which is consistent with equilibriumunder the influence of the above operative disturbance factors. Thisresulting motion will be designated as the airplane motion or simply asthe motion. The present invention is concerned with the recording of, oreiiecting control response in accordance with. this motion.

A consideration of airplane stability necessitates the establishment ofconventions, both with respect to axes and symbols, in order to setupthe equations of motion, as for example set forth in my paper Airplanelongitudinal stability, Journal of` the Aeronautical Sciences, vol. 4,pp. 61-69, Dec. 1936. The systemv herein used will be that adopted asstandard by the National Advisory Committee for Aeronautics and used inthe above-mentioned paper, as indicated in Fig. 1.

The airplane in flight has six degrees of freedom, namely, adisplacement and a rotation along or about, respectively, each of thethree axes of reference, X, Y and Z. For4 small values of any ofthesecomponents. the longitudinal or sym- -metric motion which involves adisplacement in X, a displacement in Z, and a rotation about Y may beconsidered apart from the lateral or asymmetric motion which involves adisplacement in Y, a rotation about X, and a rotation about Z.Independence of these sets of components of motion greatly simplifiesthe study of the longitudinal and lateral stability characteristics of!the airplane. The axes of reference are assumed to be ilxed in theairplane and to move with it.

'I'he magnitude of the angular velocity components about these axes andthe variation with timeof the components o f angular velocity aboutthese axes may be used as an index of the stability of the airplanemotion both longitudinal and lateral. Such amplitude-time angularvelocity records will, for stable motion, have the character of a dampedoscillation or wave form (Fig. 3). For unstable airplane motion, therecord will be either a simple divergence wherein the record simplydeparts from its equilibrium value (Fig.

' 4), or increasing oscillation in which, although the angular velocityvalue oscillates about an equilibrium value, its amplitude increaseswith time (Fig. 3*). In the unique case of neutral stability, theamplitude will remain constant with time (Fig. 5). The stability o! theairplane motion may be rated numerically by the valuation oi certainmathematical constants related to 1the oscillograms just discussed. Inparticular, such constants are the period of the oscillation P, the timeT to damp a disturbance to A amplitude and the damping coeillcient K inthe envelope equation a---CeKT (Fig. 3).

The characteristics of the airplane motion willl now be explained withreference .to Fig. 2 which diagrammatically illustrates'the character ofsuch a motion during and following a disturbance, for example adisturbance inducing yawing oscillationabout the Z axis; it will -beunderstood that pitching disturbances about axis Y and rollingdisturbances about axis X may take place in an analogous manner. v

In Fig. 2 diagram I records the angular displacementwith reference to aset course. During undisturbed night along a `straight course, theangular displacement u is zero as indicated a1, a. The airplane isdisturbed at a, which disturbance is sufficient to build up, during atransient time period ai-bi-ci in diagram II an angular velocity ofamplitude ci. From this point in Ydiagram I the airplane will swing farbeyond the angular displacement c, until it reaches point l where amaximum displacement is reached. From this point,y the airplane swingsin'opposite direction until, at 2, it swings through a point where the'displacement is zero relatively to the disturbed path leading back intothe set course, although not yet zero regarding the latter through whichthe airplane passes at 2*, and so on until the set course is approachednear 6. It will now be evident that, without any course control, theairplane would swing with displacements indicated at OD, about a pathconforming to disturbance angular deviation c indicated at DD in Fig. 2,and eventually continue along that new course at angle c to the originalcourse; thatl the conventional course control or automatic pilotgradually diminishes angle' c to zero in conformity with the ordinatesof CD, as the airplane is led back into its original course along themean path CD of the course control deviation; and that the actualinstantaneous values of the angular position will be given by theordinates of curve AD. At the top of Fig. 2 the corresponding airplanepositions are shown, and below diagram I the rudder positions effectedby the conventional course control which gives a control surfacedisplacement proportional to angular displacement of the airplane. Itshould be noted that, in accordance with the nature of the latter, thecontrol is applied to the greatest extent when the angular displacementis maximum but when the angular velocity is zero;

and conversely the opposing control setting is lzero when thedisplacement is zero, but when the is zero and exerts zero opposingtorque whenv the airplane kinetic energy is maximum is clearly notdesigned to be of value in damping the motion or as a stabilizing agent.The conventional automatic pilot which exerts an opposing torqueproportionate to angular displacement alone is such a device.

It may be stated that a torque best suited for damping the oscillationis not properly vproportionate in value to, or in phase with, the actualdisplacement, but must be related to the motion in such a manner as todissipate a maximum 'amount of kinetic energy. The characteristicscontrolling the optimum damping torque function must, therefore, bederived not from the actual angular displacement or course deviationfunction, but from its derivatives, namely the angular velocity orangular acceleration. Although the shape of the displacement oscillogramtheoretically contains these derivatives, it is practically not feasibleto utilize that oscillogram for an effective damping control, when theoscillation is initiated and any ins'trumentalities setting airplanecontrol surfaces iii-dependency on the displacement or course deviationmay he less than useless as a stabilizing agent. In'accordance with theinvention, the values of control responses best adapted to introduceeiective damping torques are controlled by instrumentalities directlydetecting displacement gradients, namely angular velocities or angularaccelerations.

It should be emphasized that the motion detected `according to theinvention and recorded, or applied for controlling the airplane flight,is not to be confused with the above-mentioned deviation from a setcourse, and that angular displacement values (as for example detected bymeans of free gyroscopes) can not be used effectively to govern thevalue of torques counteracting -oscillations about a mean path. A torqueadapted successfully to dampen the oscillation must be derived not fromthe momentary displacement value but from the momentary rate of changeof the displacement, that is from the velocity or its derivative theacceleration; in accordance with the invention, these rates or gradientsof displacement rather than the displacements themselves are directlydetected for purposes of recordation or control response.

Referring again to Fig. 2, the first derivative I of the deviation,namely the angular velocity is indicated at II, and the secondderivative, namely the acceleration at III. The corresponding controlsurface positions are indicated for I, II and III and it will now beevident that the control surface positions proportionate to themomentary velocity and acceleration values II and III and effective fordamping oscillations are quite dilerent from those proportionate to theangular displacement values I.

Generally speaking, if L, M and Nl are thel damping torques about axesX, Y, Z (see also Fig. 1), and p, q, r the angular velocities aboutthese axes, the important applied damping torques rates or stabilityderivatives will be Nr where etc. Similarly, second derivatives ofimportance I will be Lw, Lor, Maq, N.p and Nar where b dL etc. and

is the angular acceleration about axis X.

In accordance with the inventiomthe variation with time of the angularvelocity component is recorded, or employed for control purposes;

by deriving working torque values proportionate to the prevailingangular velocity from the pre- 'lil 1 a gyroscope rotates with momentumH about axis Z, that a torque is applied about axis Y, and that thegyroscope is mounted in such a l manner that precession takes place withangular velocity about axis X' (compare gyro GZ oi Fig. 6, for whichthese values are indicated). Employing the vector notation, thefollowing relation exists: l.

EXT

If only magnitudes are considered without-re- Vgard to directions, theabove relation changes into the scalar equation from which follows thewell-known'fact that a working torque corresponding to the disturbanceamplitude (proportional to M) can be derived from the precession torque(proportional to w) of a gyroscope (with constant momentum H) vAccording to the invention., a gyroscope driven with momentum H isarranged with'its axis of rotation parallel to one ofthe axes of the ve-`hicle system to be supervised, and this gyrothe angular deection of armA therefore indicates the angular velocity about axis Y which in anairplane related to the axis system as in-` dicated in Fig. lcorrespond, as pointed out above, to oscillations characteristic of thelongitudinal motion. A gyroscope arranged as indicated at GX of Fig. 6will analogously detect yawing velocity about axis' Z, characteristic'of directional and lateral or asymmetric stability. Finally, a gyro GYwill detect rolling. velocity Aabout axis X.

'iIf it is desired to study 'the airplane motion, arm A is connectedwith a device permitting the recordation of osclllograms similar forexample to Fig. 3, from which the characteristic .values T, P and K canbe derived. If, on the 5i' other hand, the airplane motion is to beautomatically `damped, the detecting gyros are connected to suitableairplane controls.

A preferred embodiment of a detecting and recording unit, as for exampleschematically show n at GZ of Fig. 6 and explained above with referenceto that ligure, will now be described in detail. l

Fig. 7 shows the three main parts of a unit. namely, the detector properin a housing I with partition 2, control knob 3, and switches |22 and|24, a battery 6, and a remote control switch box l with switches l23and |25. The

electric connections between` these devices will adjustment be describedlater with reference to Fig. 18. Housing I also has an air vent I0.

Above partition 2 are mounted (Figs. 8 and 9) gyroscope G, withprecession transmitter P, recorder R, restoring torque device D, iightsource S and film gear F. Below partition 2 are arranged driving motorM, transmission T with flywheel W, and air pump Q with air pressureconduit C leading throughpartition 2 to gyro G.

Gyro G consists of arotor II journaled at I2 in precession frame I3which is again journaled at I4 in bracket I5 screwed to partition 2. Thegyro rotor Il is designed as a turbo wheel with blades 2| suppliedthrough flexible tube C lwith compressed air from pump Q driven frommotor M by means of belt 22.

Precession frame I3 has trunnions 33, to one of which (Fig.' 11) isfastened a double armed lever 34 having on one end a pin 35 and on theother end a flat portion 36 which, together with screws 31 and 38fastened to housing I, constitutes a stop device for` limiting. theprecession movement of frame |3, j

The recording device R has (Figs. 9, 10, and 14) a base plate 4|fastened to partition,2 with brackets 42 and is provided with atransverse slot 43. On plate 4| are rotatably mounted four'fiangedguides44 carrying a scanning strip 45 with scanning: tube 46 (Fig. 14).

In order to transmit the precession from the gyroscope to the scanningstrip, a shaft I is provided which is at 52 journaled on partition 2. Toone end of shaft 5I is fastened a small fork 53 engaging pin 35- oflever 34 (Fig. 11), whereas the other end of shaft 5I carries a dou--yble armed lever 54 with fork 55 (Figs. 14 and 15) engaging scanning tube46.

The second arm of lever 54 is fastened to restoring springs 6|, 62which, as shown in Fig.

15, may be carried on the nuts 63, 64 of a screw 65 turning on a bracket66 fastened to housing I and having a, right-hand and a left-hand threadand a. thumb knob 61. Rotation of the latter adjusts the distance ofnuts 63, 64, and hence the tension of the restoring springs. The motionof lever 34 is damped by dashpot 68 with adjusting screw 69 (Fig. 11).

Instead of the above simple restoring device a more elaborate one may beused which is shown in Figs. 9, and 13. This device has likewise tworestoring springs 1I.' 12 which, however, move with their free ends bymeans of two arms 16, 11 (Fig. 13) in arcuate slots 13, 14 of a guideplate 15 vfastened to housing I. Arms 16, 11 are journaled in plate 85at 8|, 82 and connected to two vmeshing gear wheels 83, 84,respectively, one of which carries a bevel gear whee1 85 meshing withgear 86 on a shaft 81 leading to control knob 3 outside of housing I(Fig. 7) By rotating knob 3, springs 1I, 12 can be moved in theirrespective slots. l

The devices shown in Figs. 10 and 15 permit of the restoring torque forthe purpose of changing the sensitivity of the mechanism for detectingangular velocity and for varying the amplitude' of the lm record or themagnitude of airplane control response.. These devices provide a meansof varying the forcedeflection characteristics of the springs for thestated purpose without resorting to repeatedly changing the springs forthose of slightly different characteristics. 'I'his is done by arrangingthe springs so that they may be rotated fanwise with respect to theprecessing lever 54 and thus, vary the component of spring forceperpendicuaseaevs lar to the lever 54. In this way the torque opposingthe precessional motion may be increased or decreased and theprecessional amplitude correspondingly affected. Fig. 15 indicates ameans of accomplishing this. However, with this arrangement not only isthe spring angle changed but the initial tension is likewise changed asindicated in Fig. 16 which is the well-known relation between springtension and elongation. It is of interest to note that since thecharacteristie of a spring is expressed by the slope of the plot of Fig.16, that merely changing the tension of a spring will not give theeffect of using a spring of different characteristic as the sloperemains unchanged. Only the initial tension value is altered. Althoughthe simple arrangement of Fig. 15 isoften satisfactory, it is preferableto maintain the same initial spring tension for all amplitudeadjustments. The device according to Figs. 10 and 13' accomplishes thissince obviously different angular positions of springs 1| and 12 willnot changetheir initial tension. The eiect of this adjusting device isillustrated in Fig. 17, where the fanwise'spread of springcharacteristics indicates that the initial tension is always the same.

A photographie nlm strip, preferably of the common 35 mm. motion picturetype. can be carried past scanning tube 46 at uniform speed, by means ofthe following arrangement. The film ,f

is supplied from, and received on reels 9| and 92,I

respectively, and guided past slot 43 of plate 4| by meansof aconventional film sprocket 93 (Figs. 9 and 14) As shown in Figs. 8 and9, reel 92 and sprocket 93 derive their motion from motor M by means ofworm drive 95 and shaft 96, lm sprocket 93 being driven from sprocket 91on shaft 98, through geared pulley 98 meshing with sprocket 91 anddriving through belt 99 a pulley` IUI fastened to reel 92.

The illuminating device S consists of a lamp housing III with tubularlamp II2, cylindrical lens H3 and slit diaphragm I| 4 (Fig. 14) whichdirect the light from straight wirefilament IIS of lamp ||2 throughfunnel-shaped scanning tube 46 towards film f on sprocket drum 89.

As shown in Fig. 18, motor M is driven from battery I2I in casing 6 andcontrolled by two switches |22 and |23 connected in parallel, one

being mounted on housing I and the other on remote control box 1. LampI|2 is similay controlled by switches |24 and |29. As indicated in Figs.'1 and 18, battery and remote control leads are connected to the gyrohousing by means of detachable plugs |26 and |21.

In order to make records with an instrument of the above-described type,box I is fastened in the airplane in proper alignment'with the axes asexplained with reference to Fig.'6. If it is desired to makesimultaneously measurements relatively to two or three axes, two orthreeinstruments will be used; it will `be understood that two or three gyroscan be mounted in a single housing and the respective curves recorded ina single lm strip.

The battery and switch boxes having been connected according to Fig. 18,the gyro is started. preferably after the airplane is in the air. Afterthe airplaneis trimmed to an equilibrium condition, the recording lightis turned on and left running for a short time in order to provide adatum line. The airplane is then disturbed in the manner desired; afterits oscillation has cornpletely dampened out, the recorder is again leftrunning for a short time before the light is turned The ilm strip isthen removed and developed and provides an exact record of the angularvelocity or velocities about the airplane axis for which the apparatuswas orientated. f

It is understood that diierent more elaborate recording means could beemployed, as'for example such similar to sound recording equipment;however, the above described recording device was found to besatisfactory for most purposes.

If, instead of actuating a recording mechanism, the above describeddetector of angular velocity values is to be employed for governingcertain stabilizing or damping devices, as for example contro1 surfacesof an airplane, an'arrangement now to be described with reference toFigs. 19, 19 and 20 may be used.

Fig. 19 shows a hydraulic control system with an oil .pump |50, apressure tank I5|, a pressure gauge |52 controlling through aconventional electric connection |53 the drive of pump |50, a supplypipe line |545 and a return line |55. Each one of a series ofconventional slide valves IliilX, |60Y and |60Z consists of housing |6I,hollow plunger |62 with port |83, connecting rod |64, and four ports |65to |68. Ports |65 and |66 are connected to supply line |58 and returnline |55, respectively. Ports |61 and |68 are connected to ports |11 and|18, respectively, of working cylinders |10 with housings I1I, pistons|12, and connecting rods |13. The ducts |81, |88 between the valve andcylinder ports are connected through by-pass pipes |81 with cocks |82connected by a linkage |83 for joint movement. Throttle valves |89 maybe provided in connecting ducts |81, |88.

Arms A (compare Fig. 6) of precession frames I3 swinging on pivots I2and at Id supporting gyro rotors I3, are at ISI linked to connectionrods |64 of valves |60. As above explained, the three gyros will bearranged in such amanner that each precession frame `detects angularvelocities about a 'different one of the three axes X, Y, Z.

Under normal conditions, when the angular velocity is zero, piston. |62closes the ports leading to the work cylinder, as shown for valve |60Y.If a gyro detects a positive or negative angular velocity, connectionrod |64 and cylinder |62 will be moved in one direction -or the other.Considering for example valve |50X, pressure oil will be admitted at|65, iiow around the piston and through port |68, line |88 and cylinderport |18 into cylinder |1I moving piston I12towards the left. Oil fromthe left-hand side of the cylinder passes through port |11, duct |81 andport |61, flows through piston port |63, the

- hollow piston and out through port |66 back into return line |55 andpump |50.

Through a suitable linkage indicated as crank I 9|, valve rod |13rotates worm |92 which rotates worm wheel |83. A planetary gear 200 hastwo master gear wheels 20|, 202 and two planet wheels 204, 205; the twoplanets are journaled in housing 206 which rotates on the master gearwheel shafts |94 and |95. Shaft |94 is keyed to worm wheel |93 and shaft|95 to a second Worm wheel 2|3, meshing with worm 2|2 which is rotatedfor example from a crank 2|I similar to crank ISI, above, suitablyconnected at 2|5 to a conventional course control for example controlcolumn 2I8.

Planetary gear housing 206 carries a sprocket with chain drive 2I8attached to the horns 2|1 of control surface 2I8.

By means of the arrangement above described by way of example, it ispossible to add or subtract two control movements; namely the damp* ingcontrol movement initiated by gyroscopic device G and relayed throughthe hydraulic transmission with valves |60 and Work cylinders |10, andthe conventional pilot or course control from stick 2|9, which, ofcourse, can be replaced by an automatic course control of well knowntype. It will from the above description be evident that equal movementof damping and course control members in the same sense will impartmaximum movement to sprocket and chain 2I6,v whereas equal movement inopposite directions will leave the planet gears stationary; anycombination of unequal movements'on either side of the superimposingdevice will provide correct algebraic addition of the control movements.

The worm drives |92, |93 and 2|2, 2|3 are inserted in order to provideundirectional transmission; without this precaution forces effective atthe control surface might find their way back through the system andinterfere with the con,- trols.

If 2|8 is for example the rudder,lvalves I60Y and |60Z would similarlycontrol elevator and ailerons, respectively.

It will be evident that it is not necessary to provide rudder, elevatorand ailerons with automatic damping control by means of a set of threegyroscopes, three valves and three Work cylinders, as above described; aquite satisfactory combination could for example include normal pilotcontrol with interchangeable automatic course control for rudder andailerons, together with automatic precession controlled damping oflongitudinal oscillations superimposed on the 40 manual elevatorcontrol.

Cocks |82 are closed lwhen the automatic damping control is used; uponopening them the hydraulic circuit becomes short-circuited and thedamping control inoperative. This is a necessary precaution since thepilot must at` any moment be able to eliminate any controls except themanual control. Provisions may further be made for positioning workpiston |12 in central position (as shown for cylinder I1I0Y) when thehydraulic control is eliminated, and for arresting them in that positionby closing valves |89.

Valves |88 may also be used for adjusting the damping rates; bythrottling the ilow of oil from control valve to work cylinder, thetravel of piston |12 can be reduced and with it the amplitude of thedamping torque exerted by the respective control surface; thisadjustment can be applied to all surfaces simultaneously, or separatelyand to different degrees to each individual surface.

While the discharge ports I 61, |66 of valve cylinders |60 may have the,in its effect generally speaking conventional, shape shown at h of Fig.19, providing a linear relation between the movement of the precessionframe and that of the control surface, the metering edges of the portsmay be shaped to provide a non-linear relation, as shown in Fig. 19iwhere i is a curved metering port edge and i the corresponding piston orslide edge; relating these edges and the kinematic characteristics ofall mechanisms involved, any desired translation function can beobtained.

Instead of superimposing course and damping control movements upon asingle control surface,

evidently by suitably corto damping rudder 25|, damping ailerons 252 anddamping elevators 253. Auxiliary damping control surfaces of an area ofabout 25% of the total control surface area will give satisfactoryresults. The course control surfaces 255, 256 and 251 are at 26|, 262,263 linked to manual or automatic controls (not shown) in conventionalmanner. With equipment of this type any special interlocking devicesbetween course and damping controls are "unnecessary: it is merelynecessary to provide a simple device for disconnecting the automatic,damping control and for iixating the damping surfaces in neutralposition, converting them in this manner into ordinary n sur- Referringnow to arrangements dealing with the direct detection of accelerationvalues, there may be used for that purpose, according to the invention,a torsional seismic element. If a torsional seismic element be used asan indicator of the variation of 'angular acceleration of the foundationupon which it is placed (in this case an airplane) the following termsmay be defined:

A=the angular amplitude through which the foundation oscillates.

U=the system supporting the seismic element and resting upon thefoundation whose characteristics are te be measured.

1`=the angular ,deflection amplitude of oscillation of the pivotedflywheel with respect to the system U.

w=imposed angular velocity of the foundation (or airplane).

wn=natural angular frequency" of the massspring combination in freeoscillation in radi- Referring to Fig. 21, a comparatively heavy mass Qis arranged for practically frictionless rotation against a restrictingtorque represented by torsional spring S, I is the moment of inertia ofmass Q, and lc the torsional stiffness of spring S in inch-lbs. perradian.- Using the value of Io as a measure of the airsplane disturbanceamplitude A0, the following equation describes the relation betweenthese two terms:

11.: (w/ar A. l (oi/w10* If ratio Io/Ao is plotted against ratio w/wn acurve of the shape shown in Fig. 22 is obtained which indicates that forhigh w/wn values, that is for conditions where the imposed frequency wis very much higher than the natural frequency wn, the ratio ofamplitudes Ie and A0 is substantially unity so that Io will be a measureof A0. In other words, the rotation of mass Q relatively to its supportU (for example an airplane body) can be used as an equivalentfor therotation of the airplane relatively to the instantaneously fixed systemX,

Y, Z. It is a fact that the disturbance amplitude Au is directlyproportional to the acceleration amplitude. Since, therefore To is ameasure of the angular acceleration between rotating mass and support,it is also ay measure of the angular acceleration of the airplane Justas the precessional angle in a system according to Fig. 6 is a measureof the angular velocity of the airplane relatively to its mean path.

The above condition that m have a small value relatively to w isfulfilled if a very soft spring S and a relatively large amount ofinertia I are used.

Figs. 23 to 25 show a practical embodiment of such an arrangement. InFigs. 23 and 24, a heavy mass 30| is rotatably suspended within housing302, by means of shaft 303 with pivot points 304 and 305 in jewelbearings 306, 301'. A soft spiral spring 3|| is with one end fastened toflywheel 30| and with the other to housing 302. Fixed to shaft 303 is aVane 3|2; a leaf spring 3|4 prevents excessive rotation by contactingone of pins 3I5 and 3|6 fastened to cover plate 322 of housing 302.'Ihree tubes lead through cover plate 322, exhaust tube 325 being freeof vane 3|2, whereas the tubes 326, 321 end very close to the adjacentsurface of vane 3|2. 'lubeV 325 is connected to a vacuum pump, whereas`tubes 326 and 321 lead to opposite sides of diaphragm box or pneumaticrelay 33| (Fig. 25). Diaphragm 332 is attached to connecting rod 333 ofa valve. |60 similar to those shown in Fig. 19 and controlling thepiston movement of a work cylinder |10 in the manner above explained.`

With vane 3|2 in normal position, as shown in Fig. 24, the air pressurewill be equal on both sides of diaphragm 332 and valve |60 will be atrest. Any movement of wheel 30| will change the relative opening oftubes 326 and 321, de-

40 fleeting diaphragm 332 and actuating control valve |60.

Byattaching the piston rod |13 to a control gear of the type as forexample shown in Figs. 19 and 20, damping torques derived from theangular Aacceleration values -of the airplane relative to its meancourse, can be superimposed on the pilot or course control torques.

It will be understood that arrangements different from those shown inFigs. 23 and 24 can be used, as long as they are suitable for directlydetecting acceleration values. Also, the vacuum linkage between mass Qand control valve |60 is. of course, only an example of provisionssuitable for the same purpose.

If it is desired -to make records of acceleration values instead ofemploying them for controlling vehicle movements, apparatus of the typeshown in Figs. 23 and 24 is connected to a recording device as forexample shown in Fig. 14. Tie rod 333 (Fig. 25) will then be linked toslide 45 (Fig. 14); the operation of a recorder of this type isanalogous to that described above for velocity recordation and thereforedoes not require detailed explanation.

It should be understood that the present disclosure is for the purposeof illustration only and that this invention includes all modificationsand equivalents which fall Within the scope of the appended claims.

I claim:

1. Apparatus for recording the motion of a vehicle about a selected oneof its three characteristic axes comprising means, mounted on saidvehicle, for directly detecting the continuously varying 'value of a.time derivative of the component, about said selected axis, of saidmotion,

means responding to said torque for moving said marking means relativelyto said material.

2. In apparatus for recording the motion of a vehicle about a selectedone of its three characteristic axes of rotation the combination of a Vprecession frame mounted on said vehicle for rotation about one of saidaxes, a' gyroscope 'mounted in said frame for rotation about a secondaxis, means applyingv to .said frame a. restoring torque, means fordriving said gyroscope with substantially constant momenv tum, and meansfor continuously recording the precessional travel of said frame as afunction of the tantaneou's-yalue of the vehicle about the third axis.

3. In apparatus for recording the motion of a vehicle about a selectedone of its three characangular velocity teristio axes of rotation, thecombination of a precession frame mounted on said vehicle for rotationabout one of said axes. a gyroscope mounted in said frame for rotationabout a second axis, means applying to said frame a-restoring torque,

means for driving said gyroscope with substantially constant momentum, arecord receiving surface. and means adapted to move relatively to saidsurface for marking the movement of said frame on said surface, wherebyavrecord of the angular velocity of the vehicle about the third axis canbe obtained.

4. A restoring torque device for use with gyroscopic apparatus 'having aprecession frame swinging on a support, comprising an arm attached tosaid frame, a'base attached to said support,-two levers havingrespective ends rotatably fastened to said base, two springs extendingfrom ,the respectiveother ends of said levers 'to said arm and means forrotatory adjustment of said levers relatively to said base, .saidadjustment varying the gradient ot the force exerted by said springs onsaid arm with deviation of said frame without substantially varying thevalue of said force atnormal position of said frame.

5. In a restoring torque device for use with gyroscopic .apparatushaving a precession frame swinging on a support, two resilientspring-like members attached to said frame, extending to two spacedpoints of said support, and applying substantially equal forces to theframe in normal position, and adjusting means for oppositely rotatingthe support ends of said members about' the respective frame endsthereof, said adjusting rotation varying the gradient of said forcesexerted on said frame upon deviation of the trame.-

